DSL-504 ADSL Router User’s Guide
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One of the most important elements of any network security implementation is the firewall. Packet filtering is a
basic firewall sec urity measure and should be used on any network that is exposed to security risk. A packet
filter system examines data packets and scrutinizes them in o rder to control network access. Filterin g rules
determine whether packets are passed through the Router from either side of t he gateway. The rules are created
and controlled by the network administrator and can be precisely defined. These r ules are used to block access to
the LAN from outside the network and/or to deny access to the WAN fro m within the network. The Router uses
filtering rules to exa mine data packet header s for specific infor mation. Packets passing through the Router that
do not meet the criteria specified by the rule set are dropped.
In order to improve network security without severely limiting network efficiency, it is important to carefully
plan the sets of access rules. Effective implementation of packet filtering requires detailed kno wledge of network
services and communication protocols. An overly complicated filtering scheme can adversely affect Router
performance, while an inadequate set of rules may needlessly compromise security.
Filtering rules can be precisely defined based upon source and destination IP address, as well as port and
protocol information.
Figure 4 - 10. Filter & Firewall Main Menu
The Existing Entry number tells you how many routes are currently configured. The Valid Entry number tells
you the number of routes that are enabled. Filtering can be universally enabled or disabled with the d rop-down
IP Filter State drop-down menu.